Starting method of high-pressure water electrolysis system and starting method of water electrolysis system

ABSTRACT

A starting method includes determining whether a depressurizing current was supplied to a water electrolyzer while at least a cathode side of the water electrolyzer was depressurized in an immediately previous stop of a water electrolysis system after electrolyzing water. A first current is supplied to the water electrolyzer at a first supply rate to start the water electrolysis system in a case where it is determined that the depressurizing current was supplied to the water electrolyzer in the immediately previous stop. A second current is supplied to the water electrolyzer at a second supply rate lower than the first supply rate to start the water electrolysis system in a case where it is determined that the depressurizing current was not supplied to the water electrolyzer in the immediately previous stop.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2016-098866, filed May 17, 2016, entitled “Starting Method of High-pressure Water Electrolysis System.” The contents of this application are incorporated herein by reference in their entirety.

BACKGROUND 1. Field

The present disclosure relates to a starting method of a high-pressure water electrolysis system and a starting method of a water electrolysis system.

2. Description of the Related Art

In general, hydrogen is used as fuel gas for power generation in a fuel cell. Hydrogen is produced by a water electrolysis system that incorporates a water electrolysis device, for example. The water electrolysis device produces hydrogen (and oxygen) by electrolyzing water and thus uses a solid polymer electrolyte membrane (ion exchange membrane).

Electrode catalyst layers are provided on both sides of an electrolyte membrane, and an electrolyte-membrane-electrode structure is thereby configured. Further, power feeders are disposed on both sides of the electrolyte-membrane-electrode structure, and a water electrolysis cell is thereby configured.

Here, in the water electrolysis device in which plural water electrolysis cells are laminated, a voltage is applied to both ends in a laminating direction, and water is supplied to an anode power feeder. Thus, on an anode side of the electrolyte-membrane-electrode structure, water is decomposed, and hydrogen ions (protons) are generated. The hydrogen ions permeate the solid polymer electrolyte membrane and move to a cathode side and are bonded to electrons to produce hydrogen in a cathode power feeder.

The hydrogen led out from the water electrolysis device is delivered to a gas-liquid separation device, and liquid water is removed. Subsequently, the hydrogen is supplied to a hydrogen purification unit (water adsorption unit), and product hydrogen (dry hydrogen) is obtained. Meanwhile, on the anode side, oxygen generated together with the hydrogen is discharged from the water electrolysis device while accompanying excess water.

As the water electrolysis device, a high-pressure water electrolysis device (differential pressure type water electrolysis device) may be employed which generates hydrogen at a high pressure (in general, 1 MPa or higher) on the cathode side. In the high-pressure water electrolysis device, while high-pressure hydrogen is filled in a fluid path of a cathode separator across the electrolyte membrane, water and oxygen at a normal pressure are present in a fluid path of an anode separator. Accordingly, in a case of an operation stop (an end of supply of generated hydrogen), the pressure difference between both sides of the electrolyte membrane has to be removed in order to protect the electrolyte membrane.

Accordingly, in related art, Japanese Unexamined Patent Application Publication No. 2010-236089 discloses an operation stop method of a water electrolysis device, for example. This operation stop method includes a step of applying a voltage after supply of hydrogen from a cathode-side electrolysis chamber is stopped and a step of performing depressurization of at least the cathode-side electrolysis chamber in a state where the voltage is applied. Japanese Unexamined Patent Application Publication No. 2010-236089 discusses that because this electrolysis depressurization process causes hydrogen that leaks from the cathode side to an anode side to return to the cathode side by a hydrogen membrane pump effect, and stagnation of leaked high-pressure hydrogen may be restrained, and degradation of a catalyst electrode due to hydrogen may be inhibited.

SUMMARY

According to one aspect of the present invention, a starting method of a high-pressure water electrolysis system that includes a high-pressure water electrolysis device which electrolyzes supplied water, produces oxygen on an anode side, and produces hydrogen at a higher pressure than the oxygen on a cathode side, the starting method includes a step of determining whether or not depressurization on at least the cathode side is performed while a depressurizing current is applied in a previous stop of the high-pressure water electrolysis system. The starting method includes a step of performing starting by applying a starting current to the high-pressure water electrolysis device at a normal current application rate in a case where a determination is made that an electrolysis depressurization process, in which depressurization is performed while the depressurizing current is applied, is performed in the previous stop. The starting method includes a step of performing the starting by applying the starting current to the high-pressure water electrolysis device at a current application rate that is lower than the normal current application rate in a case where a determination is made that an electroless depressurization process, in which depressurization is performed while the depressurizing current is not applied, is performed in the previous stop.

According to another aspect of the present invention, a starting method of a water electrolysis system including a water electrolyzer, the starting method includes determining whether a depressurizing current was supplied to the water electrolyzer while at least a cathode side of the water electrolyzer was depressurized in an immediately previous stop of the water electrolysis system after electrolyzing water to produce oxygen with a first pressure on an anode side and hydrogen with a second pressure higher than the first pressure on the cathode side. A first current is supplied to the water electrolyzer at a first supply rate to start the water electrolysis system in a case where it is determined that the depressurizing current was supplied to the water electrolyzer in the immediately previous stop. A second current is supplied to the water electrolyzer at a second supply rate lower than the first supply rate to start the water electrolysis system in a case where it is determined that the depressurizing current was not supplied to the water electrolyzer in the immediately previous stop.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings.

FIG. 1 is a schematic configuration explanatory diagram of a high-pressure water electrolysis system that employs a starting method according to this embodiment of the present disclosure.

FIG. 2 is a flowchart for explaining the starting method.

FIG. 3 is a timing diagram for explaining the starting method.

FIG. 4 is a timing diagram of a case where a normal current application rate is employed in the starting method.

DESCRIPTION OF THE EMBODIMENTS

The embodiments will now be described with reference to the accompanying drawings, wherein like reference numerals designate corresponding or identical elements throughout the various drawings.

As illustrated in FIG. 1, a high-pressure water electrolysis system 10 according to an embodiment of the present disclosure includes a high-pressure water electrolysis device 12. The high-pressure water electrolysis device 12 electrolyzes water (pure water) and thereby produces oxygen and high-pressure hydrogen (at a higher pressure than an oxygen pressure that is a normal pressure, for example, hydrogen at 1 to 80 MPa).

In the high-pressure water electrolysis device 12, plural water electrolysis cells 14 are laminated, and end plates 16 a and 16 b are disposed at both ends in a laminating direction of the water electrolysis cell 14. An electrolysis power source 18 that is a direct current power source is connected with the high-pressure water electrolysis device 12. A water supply line 20 that communicates with an anode inlet side (water supply inlet side), which is not illustrated, is connected with the end plate 16 a.

A water discharge line 22 that communicates with an anode outlet side (water and generated oxygen discharge side) and a hydrogen lead-out line 24 that communicates with a cathode side (high-pressure hydrogen generating side) are connected with the end plate 16 b. Oxygen that is generated by a reaction (and permeating hydrogen) and unreacted water are discharged to the water discharge line 22.

The water supply line 20, on which a circulating water pump 26 and a cooling apparatus 27 are arranged, is connected with a bottom portion of an oxygen gas-liquid separation apparatus 28. An air blower 30 and the water discharge line 22 communicate with an upper portion of the oxygen gas-liquid separation apparatus 28. A pure water supply line 34 that is connected with a pure water producing device 32 and a gas discharge line 36 for discharging oxygen and hydrogen that are separated from the pure water by the oxygen gas-liquid separation apparatus 28 is coupled with the oxygen gas-liquid separation apparatus 28.

The hydrogen lead-out line 24 connects the high-pressure water electrolysis device 12 with a high-pressure hydrogen gas-liquid separation apparatus 38. High-pressure hydrogen from which water is removed by the high-pressure hydrogen gas-liquid separation apparatus 38 is led out to a high-pressure hydrogen supply line 40. The high-pressure hydrogen supply line 40 is provided with a back pressure valve 42 that is set to a predetermined pressure value (for example, 70 MPa).

A water draining line 46 that discharges liquid water separated by the high-pressure hydrogen gas-liquid separation apparatus 38 is connected with a lower portion of the high-pressure hydrogen gas-liquid separation apparatus 38. On the water draining line 46, a first solenoid valve 48 and a drained water depressurization mechanism that applies pressure loss and thereby causes the liquid water of a set water amount to flow through, for example, an orifice 50 are disposed along a flow direction of the liquid water. Instead of the orifice 50, a reducing valve may be used, for example.

The water draining line 46 is connected with a low-pressure gas-liquid separation apparatus 52, which performs gas-liquid separation of the liquid water at a lowered pressure, in a downstream portion of the orifice 50. The low-pressure gas-liquid separation apparatus 52 and the oxygen gas-liquid separation apparatus 28 are connected together by a water returning line 56. A second solenoid valve 58 is disposed on the water returning line 56.

An upper side of the high-pressure hydrogen gas-liquid separation apparatus 38 and an upper side of the low-pressure gas-liquid separation apparatus 52 are connected together by a pressure releasing line 60 that discharges gas (hydrogen) separated in the low-pressure gas-liquid separation apparatus 52. On the pressure releasing line 60, a depressurization mechanism, for example, a reducing valve 62 and a third solenoid valve 64 are disposed along a high-pressure hydrogen flow direction.

On the water discharge line 22, a hydrogen sensor 66 that detects the hydrogen concentration in discharged fluids (oxygen, hydrogen, and water vapor) is disposed. Detection results that are obtained by the hydrogen sensor 66 are transmitted to a controller 68, and the controller 68 performs operation control of the whole high-pressure water electrolysis system 10.

An action of the high-pressure water electrolysis system 10 configured as described above will be described below.

First, in a case of a starting operation of the high-pressure water electrolysis system 10, pure water that is generated from city water via the pure water producing device 32 is supplied to the oxygen gas-liquid separation apparatus 28. Then, by work of the circulating water pump 26, the pure water in the oxygen gas-liquid separation apparatus 28 is supplied to the anode inlet side of the high-pressure water electrolysis device 12 via the water supply line 20. Meanwhile, a voltage is applied to the high-pressure water electrolysis device 12 via the electrolysis power source 18 that is electrically connected therewith, and the electrolytic current is applied to the high-pressure water electrolysis device 12.

Thus, in each of the water electrolysis cells 14, pure water is decomposed by electricity on the anode side, and hydrogen ions, electrons, and oxygen are generated. Accordingly, on the cathode side, hydrogen is obtained by bonding of hydrogen ions to electrons, and the hydrogen is taken out to the hydrogen lead-out line 24.

Meanwhile, on the anode outlet side, the oxygen generated by the reaction, the unreacted water, and the permeated hydrogen dynamically flow, and those mixed fluids are discharged to the water discharge line 22. The unreacted water, oxygen, and hydrogen are introduced to the oxygen gas-liquid separation apparatus 28 and separated. Subsequently, the water is introduced to the water supply line 20 via the circulating water pump 26. The oxygen and hydrogen that are separated from the water are discharged from the gas discharge line 36 to the outside.

Hydrogen generated in the high-pressure water electrolysis device 12 is delivered to the high-pressure hydrogen gas-liquid separation apparatus 38 via the hydrogen lead-out line 24. In the high-pressure hydrogen gas-liquid separation apparatus 38, the liquid water contained in hydrogen is separated from the hydrogen and stored. Meanwhile, the hydrogen is led out to the high-pressure hydrogen supply line 40. The pressure of the hydrogen is raised to a set pressure (for example, 70 MPa) of the back pressure valve 42. Subsequently, the hydrogen is dehumidified by a dehumidifying device or the like, which is not illustrated, becomes dry hydrogen (product hydrogen), and is supplied to a fuel cell electric vehicle or the like.

Next, in a case where an electrolysis operation of the high-pressure water electrolysis system 10 is stopped, the controller 68 starts a pressure releasing process of the high-pressure water electrolysis device 12. Specifically, because the third solenoid valve 64 is opened, the high-pressure hydrogen that is filled on the cathode side is depressurized while passing from the hydrogen lead-out line 24 through the pressure releasing line 60 and is subsequently discharged to the low-pressure gas-liquid separation apparatus 52.

In this case, an electrolytic current that is lower than the above electrolytic current (hereinafter also referred to as depressurizing current) is applied by the electrolysis power source 18 (electrolysis depressurization process). The depressurizing current is set to a minimum current value by which a membrane pump effect is obtained, for example.

Then, in a case where the hydrogen pressure on the cathode side becomes the same pressure as the pressure (normal pressure) on the anode side, voltage application by the electrolysis power source 18 is stopped. Accordingly, the operation of the high-pressure water electrolysis system 10 is stopped.

Next, a starting method of the high-pressure water electrolysis system 10 according to the embodiment of the present disclosure will be described along a flowchart illustrated in FIG. 2.

The controller 68 determines whether the above electrolysis depressurization process is preformed or the electroless depressurization process is performed in the previous operation stop of the high-pressure water electrolysis system 10 (step S1). The electroless depressurization process is a process for depressurization without performing application of the electrolytic current in a case where abnormality occurs in an operation of the high-pressure water electrolysis system 10 and an emergency stop of the high-pressure water electrolysis system 10 is performed.

In a case where the controller 68 determines that the electroless depressurization process is performed in the previous operation stop of the high-pressure water electrolysis system 10 (YES in step S1), the process moves to step S2. In step S2, water is caused to circulate for only a prescribed time (for example, 5 seconds) after the circulating water pump 26 is driven (ON). That is, before starting applying a starting current (electrolytic current) to the high-pressure water electrolysis device 12, an inside of the high-pressure water electrolysis device 12 is filled with water.

Further, moving to step S3, the application of the starting current to the high-pressure water electrolysis device 12 is started at a prescribed current application rate (for example, 0.5 A/second) (hereinafter also referred to as corrected current application rate). The corrected current application rate is set to a lower rate than the current application rate (hereinafter also referred to as normal current application rate) in a case where the electrolysis depressurization process is performed in the previous operation stop (NO in step S1). Here, the current application rate represents a current raising rate (change rate) in a case where the staring current is raised to a rated current value.

As illustrated in FIG. 3, in a case where the emergency stop of the high-pressure water electrolysis system 10 is performed, because depressurization by membrane permeation is performed without water circulation, hydrogen is likely to stagnate on the anode side. Accordingly, the starting current is applied to the high-pressure water electrolysis device 12 at the corrected current application rate when the high-pressure water electrolysis system 10 is started, and the hydrogen concentration of the fluid that is discharged to the water discharge line 22 of the high-pressure water electrolysis device 12 may thereby be suppressed to a certain concentration or lower. Here, the certain concentration is a concentration of 1%, for example.

That is, the oxygen amount that is generated from the high-pressure water electrolysis device 12 in the starting at a time after the electroless depressurization process is reduced compared to the oxygen amount that is produced in the normal starting at a time after the electrolysis depressurization process. Thus, the hydrogen that stagnates on the anode side due to the electroless depressurization process is not discharged from the high-pressure water electrolysis device 12 at one time. Accordingly, in this embodiment, effects of enabling the hydrogen concentration in the discharged fluid to be suppressed to the certain value or lower and enabling an efficient high-pressure water electrolysis process to be certainly achieved are obtained.

Meanwhile, FIG. 4 illustrates a starting method of applying the starting current to the high-pressure water electrolysis device 12 at the normal current application rate in the starting in a case where the electroless depressurization process is performed in the previous operation stop. Accordingly, because oxygen that is produced from the high-pressure water electrolysis device 12 in the starting is much, the hydrogen concentration in the fluid that is discharged from the anode side temporarily rises and becomes a concentration exceeding 1%, for example, and the stop of starting may be caused.

As illustrated in FIG. 3, in a case where the starting current is applied to the high-pressure water electrolysis device 12 at the corrected current application rate, the hydrogen concentration of the hydrogen discharged from the high-pressure water electrolysis device 12 temporarily rises and subsequently drops. In a case where the hydrogen concentration becomes lower than a predetermined concentration (for example, 0.2%) after a prescribed time elapses or the hydrogen concentration temporarily rises (YES in step S4), the process moves to step S5. In step S5, the starting current value is raised to the rated current value at the normal current application rate for the high-pressure water electrolysis device 12. Thus, a high-pressure water electrolysis operation by the high-pressure water electrolysis system 10 is started.

Further, in this embodiment, before starting applying the starting current (electrolytic current) to the high-pressure water electrolysis device 12, the water is caused to circulate only in the prescribed time (for example, 5 seconds) in which the inside of the high-pressure water electrolysis device 12 is filled with the water. Accordingly, a case where the hydrogen concentration rises may properly be handled.

In addition, while the starting current is applied to the high-pressure water electrolysis device 12 at the corrected current application rate that is lower than the normal current application rate, the hydrogen concentration in the fluid discharged from the anode side of the high-pressure water electrolysis device 12 is detected. Further, in a case where the detected hydrogen concentration becomes a prescribed value or lower, the starting current value of the current that is applied to the high-pressure water electrolysis device 12 is raised to the rated current value. Accordingly, it is possible to quickly raise the pressure of hydrogen generated by the high-pressure water electrolysis device 12.

Furthermore, as a start pressure of the electroless depressurization process is higher in the previous emergency stop, the current application rate is set lower. The amount of hydrogen that stagnates on the anode side changes depending on the start pressure of the electroless depressurization process. Thus, in accordance with the estimated hydrogen amount that stagnates on the anode side, the current application value is changed, and it is thereby possible to certainly suppress the rise of the hydrogen concentration of the discharged hydrogen and to inhibit an unnecessary time for the starting from being provided.

The present disclosure relates to a starting method of a high-pressure water electrolysis system that includes a high-pressure water electrolysis device which electrolyzes supplied water, produces oxygen on an anode side, and produces hydrogen at a higher pressure than the oxygen on a cathode side.

This starting method includes a step of determining whether or not depressurization on at least a cathode side is performed while a depressurizing current is applied in a previous stop of a high-pressure water electrolysis system. The starting method includes a step of performing starting by applying a starting current to the high-pressure water electrolysis device at a normal current application rate in a case where a determination is made that an electrolysis depressurization process, in which depressurization is performed while the depressurizing current is applied, is performed in the previous stop.

The starting method includes a step of performing the starting by applying the starting current to the high-pressure water electrolysis device at a current application rate that is lower than the normal current application rate in a case where a determination is made that an electroless depressurization process, in which depressurization is performed while the depressurizing current is not applied, is performed in the previous stop.

Further, in the starting method, before starting applying the starting current to the high-pressure water electrolysis device, water is preferably caused to circulate only in a prescribed time in which an inside of the high-pressure water electrolysis device is filled with the water.

In addition, the starting method preferably further includes a step of detecting a hydrogen concentration in a fluid that is discharged from an anode side of the high-pressure water electrolysis device while the starting current is applied to the high-pressure water electrolysis device at the current application rate. Further, the starting method preferably further includes a step of raising a starting current value of a current that is applied to the high-pressure water electrolysis device to a rated current value in a case where the detected hydrogen concentration becomes a prescribed value or lower.

Furthermore, in the starting method, as a start pressure of the electroless depressurization process is higher, the current application rate is preferably set lower.

In the techniques of the present disclosure, in a case where the electroless depressurization process is performed, the starting is performed in a state where the current application rate of a current applied to the high-pressure water electrolysis device is set lower than the normal current application rate in a case where a determination is made that depressurization is performed while the depressurizing current is applied.

Accordingly, the oxygen amount that is generated in the starting at a time after the electroless depressurization process is reduced compared to the oxygen amount that is produced in normal starting at a time after the electrolysis depressurization process. Thus, the hydrogen that stagnates on the anode side due to the electroless depressurization process is not discharged from the high-pressure water electrolysis device at one time. Accordingly, the hydrogen concentration in the discharged fluid may be suppressed to the certain value or lower, and an efficient differential pressure type water electrolysis process may be achieved.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein. 

What is claimed is:
 1. A starting method of a high-pressure water electrolysis system that includes a high-pressure water electrolysis device which electrolyzes supplied water, produces oxygen on an anode side, and produces hydrogen at a higher pressure than the oxygen on a cathode side, the starting method comprising: a step of determining whether or not depressurization on at least the cathode side is performed while a depressurizing current is applied in a previous stop of the high-pressure water electrolysis system; a step of performing starting by applying a starting current to the high-pressure water electrolysis device at a normal current application rate in a case where a determination is made that an electrolysis depressurization process, in which depressurization is performed while the depressurizing current is applied, is performed in the previous stop; and a step of performing the starting by applying the starting current to the high-pressure water electrolysis device at a current application rate that is lower than the normal current application rate in a case where a determination is made that an electroless depressurization process, in which depressurization is performed while the depressurizing current is not applied, is performed in the previous stop.
 2. The starting method according to claim 1, wherein before starting applying the starting current to the high-pressure water electrolysis device, water is caused to circulate only in a prescribed time in which an inside of the high-pressure water electrolysis device is filled with the water.
 3. The starting method according to claim 1, further comprising: a step of detecting a hydrogen concentration in a fluid that is discharged from the anode side of the high-pressure water electrolysis device while the starting current is applied to the high-pressure water electrolysis device at the current application rate; and a step of raising a starting current value of a current that is applied to the high-pressure water electrolysis device to a rated current value in a case where the detected hydrogen concentration becomes a prescribed value or lower.
 4. The starting method according to claim 1, wherein as a start pressure of the electroless depressurization process is higher, the current application rate is set lower.
 5. A starting method of a water electrolysis system including a water electrolyzer, the starting method comprising: determining whether a depressurizing current was supplied to the water electrolyzer while at least a cathode side of the water electrolyzer was depressurized in an immediately previous stop of the water electrolysis system after electrolyzing water to produce oxygen with a first pressure on an anode side and hydrogen with a second pressure higher than the first pressure on the cathode side; supplying a first current to the water electrolyzer at a first supply rate to start the water electrolysis system in a case where it is determined that the depressurizing current was supplied to the water electrolyzer in the immediately previous stop; and supplying a second current to the water electrolyzer at a second supply rate lower than the first supply rate to start the water electrolysis system in a case where it is determined that the depressurizing current was not supplied to the water electrolyzer in the immediately previous stop.
 6. The starting method according to claim 5, wherein before starting supplying the first or second current to the electrolyzer, water is caused to circulate only in a prescribed time in which an inside of the electrolyzer is filled with the water.
 7. The starting method according to claim 5, further comprising: detecting a hydrogen concentration in a fluid that is discharged from the anode side while the first or second current is supplied to the electrolyzer; and raising a starting current value of a current that is applied to the electrolyzer to a rated current value in a case where the detected hydrogen concentration becomes a prescribed value or lower.
 8. The starting method according to claim 5, wherein as a start pressure of an electroless depressurization process is higher, the first supply rate or the second supply rate is set lower. 